For example, in a plasma etching apparatus for performing dry etching on a semiconductor wafer, an inner space of a processing chamber where the semiconductor is actually etched is constantly maintained in a vacuum environment. Meanwhile, the semiconductor wafer to be etched is loaded into the plasma etching apparatus while being accommodated in a FOUP (Front Opening Unified Pod) in an atmospheric atmosphere, for example.
The plasma etching apparatus includes a mounting unit for mounting thereon a FOUP in an atmospheric atmosphere, and a transfer chamber whose environment can be switched between a vacuum state and an atmospheric state is provided between the mounting unit and the processing chamber in order to load and unload the semiconductor wafer between the FOUP and the processing chamber (e.g., Japanese Patent Application Publication No. 2002-353086 (Patent Document 1)).
A first and a second gate valve are provided between the mounting unit and the transfer chamber and between the transfer chamber and the processing chamber, respectively. When the atmosphere of the inner space of the transfer chamber is in the atmospheric environment, the first gate valve is opened while closing the second valve. In that state, the semiconductor wafer is loaded from the FOUP into the transfer chamber and, then, the first gate valve is closed. Next, the transfer chamber is depressurized to a pressure substantially equal to that in the processing chamber. Thereafter, the second gate valve is opened while closing the first gate valve. In that state, the semiconductor wafer is loaded from the transfer chamber into the processing chamber. Then, the second gate valve is closed, and an etching process is performed in the processing chamber. Next, the semiconductor wafer is transferred from the processing chamber to the FOUP in a reverse sequence of the above-described operation.
In the above series of the processing, the adhesion of particles to the semiconductor wafer in the transfer chamber becomes a problem as a pattern of semiconductor devices formed on the semiconductor wafer becomes more miniaturized. Therefore, in the aforementioned Patent Document 1, a charge neutralizer for generating an ion stream is provided in the transfer chamber in order to remove particles adhered to an inner wall of the transfer chamber (referred to as an “air lock chamber” in the Patent Document 1).
Here, the charge neutralizer emits the ion stream to the transfer chamber and neutralizes the charge of the particles adhered by electrostatic force (Coulomb force) to the inner wall of the transfer chamber by using ions in the ion stream (elimination of static electricity) so that the particles can be separated from the inner wall. Next, the particles are removed from the transfer chamber by discharging gas in the transfer chamber to the outside by a suction unit.
Moreover, in the Patent Document 1, after the particles adhered to the inner wall of the transfer chamber are discharged and removed, the semiconductor wafer is loaded into the transfer chamber. Then, the electrically charged particles adhered to the semiconductor wafer are attracted onto the electrode by applying a voltage, while considering an electrically charged state of the semiconductor wafer, to an electrode disposed above the semiconductor wafer.
Although a specific method for generating ions by the charge neutralizer provided in the transfer chamber is not described in the Patent Document 1, it may be considered that a corona discharge is used as an excellent method to generate positive ions and negative ions while maintaining an ion balance. In addition, UV irradiation or X-ray irradiation may be used as a method to generate ions.
However, in the ion generation method using the corona discharge, particles may be also generated by the corona discharge and the particles thus generated may remain in the transfer chamber to be adhered to the semiconductor wafer loaded into the transfer chamber.
Moreover, in the Patent Document 1, an additional electrode for electrostatically attracting particles is provided above the semiconductor wafer in order to remove the particles adhered to the semiconductor wafer. In that case, a power supply for applying a high voltage to the electrode is required and, therefore, the configuration and the control of the apparatus become complicated.
As can be clearly seen from the above-described configuration, the charge of the semiconductor wafer is not directly neutralized in the transfer chamber described in the Patent Document 1. For example, the semiconductor wafer is electrically charged by the processing such as plasma etching or the like, so that the particles are easily attracted to the charged semiconductor wafer by the electrostatic force when the charged semiconductor wafer returns to the transfer chamber in the depressurized environment. Further, the semiconductor wafer may be electrically charged when the semiconductor wafer in the atmospheric environment is loaded into the transfer chamber in the atmospheric environment.
The adhesion of particles to the semiconductor wafer by the electrostatic force is facilitated as a particle diameter of the particles decreases. Accordingly, in order to cope with a trend towards a fine pattern of other semiconductor devices, the adhesion of fine particles to the semiconductor wafer which is not a problem in manufacturing semiconductor devices in a prior art needs to be prevented by neutralizing the charge of the semiconductor wafer and preferably by neutralizing the charge of the particles on the semiconductor wafer.
Overall, in the technique described in the Patent Document 1, the charge of the semiconductor wafer can be neutralized by the ions generated by the charge neutralizer. However, when the ion generation method using a corona discharge is used, the particles generated by the corona discharge may be adhered to the semiconductor wafer, or it may be difficult to control the corona discharge at a low pressure. Further, in the ion generation method using UV irradiation or X-ray irradiation, the semiconductor wafer may be damaged by the UV irradiation or the like to the semiconductor wafer.